In-ground storage facility with footing sections and method of installing the same



Dec. 20, 1966 F. J. SANGER 3,292,377

TN-OEOUNO STORAGE FACILITY wTTE EOOTTNO SECTIONS AND METHOD OE TNSTALETNG TEE SAME o o o INVENTOR Frederick J. Sanger ATTORNEY Dec. 20, 1966 F. J. SANGER 3,292,377

IN-GROUND STORAGE FACILITY WITH FOOTING SECTIONS AND METHOD OF INSTALLING THE SAME Filed April 9, 1954 2 Sheets-sheet a FIG. 4.v

INVENTOR Frederick J. Sanger ATTORNEY United States Patent O 3,292,377 IN-GROUND STORAGE FACILITY WITH FUOT- ING SECTINS AND METHGD F INSTALLING THE SAME Frederick J. Sanger, Hanover N.H., assignor to Couch International Methane Limited, Nassau, Bahamas Filed Apr. 9, 1964, Ser. No. 358,421 7 Claims. (Cl. 61-.5)

This invention relates to in-ground storage of liquid gases, i.e., the storage of liquid gases at very low ternperatures in a roofed-in open excavation in the ground, and has for its primary purpose the provision of a novel type lof wall and footings for a liquid-and-gas-tight wall surrounding the upper portion of such an excavation.

There is a need in modern gas'technology for storing very large quantities of fuel vgas in liquid form, commonly LNG (liquid natural gas consisting chiey of methane gas), at locations accessible to large-scale industrial and general users of such fuels. A recent technique for providing such storage consists ofso-called in-ground storage reservoirs, which are essentially large pits excavated in the surface of the ground by techniques generally similar to those used in excavating for large-scale substructures. These reservoirs are typically more than a hundred feet across by more than a hundred feet deep. They are covered with a liquid-and-gas-tight roof which issuitably insulated, and used to store the liquid gas at temperatures from 40 F. to 258 F. or even lower. Where these excavations are made in saturated soil, the natural moisture in the soil freezes to provide a fluid-tight frozen wall of great thickness, typically 10-20 feet, which serves also as a fluid-tight insulating barrier to retain the extremely low temperature of the fluid. In typical situations in the United States and in many other parts of the world, the terrain in which the hole is dug consists of a relatively thin overburden of soil ranging from -50 feet in thickness, resting upon a comparatively hard and impervious stratum of rock. The necessary excavation thus extends not only through the overburden of soil, but also extends well into the rock, in some cases for 150 feet or more. The overlying soil portion of the excavation typically contains water up to the level of the water table in that particular area, but except during or after heavy rains, the ground very near the surface is usually relatively dry and does not contain suicient moisture to form a reliable liquid seal upon freezing. It is therefore desirable and even necessary in many locations to provide an impervious wall at the upper portion of the in-ground excavation to insure proper retention of the fluid and the gaseous vapor contents stored in the reservoir. This wall may be made of a number of suitable materials, but usually the cheapest material for the purpose is concrete. However, a concrete wall is very heavy, and must be set upon proper footings in order to be adequately supported. Under the conditions frequently encountered in practice, this presents surprising difficulties.

A preferred method of making the above-described excavation, at least at the top portion where soil must be removed, is to freeze a large annulus of soil circumscribing the desired excavation, and then to remove the earth from within the annulus. This technique ensures maintenance of a rigid soil structure outside of the excavated portion, without the necessity of timbering or sheet piling the earth walls of the reservoir to prevent collapse or inward sliding, and obviates pumping. It must be remembered that in normal use this earth will be maintained far below freezing temperature by the contents, and it is therefore only necessary to initially pre-freeze the soil and to maintain it frozen until the completed reservoir is filled with liquid gas.

The above circumstances deline the, environment in FPice which footings must be provided for the above-described heavy wall at the upper yperimeter of the excavation. Normally, poured concrete footings would be used, but if this were done before the soil is frozen, there is a virtual certainty that the footings will move differentially in the soil as the excavation proceeds because of irregular volume changes of the soil in freezing. On the other hand, if the concrete is poured after the soil is frozen, the temperature is so low that the cement will not harden properly; at the same time, while the cement is setting, the heat `of hydration will tend to damage the frozen soil by thawing it. VIt is a major object of the invention to obviate this diiculty by the use of pre-cast, pre-stressed concrete blocks of a special construction, which are embedded in a special mixture so that they can be properly aligned at low temperatures, as will be described below.

Another object is to provide footings for a heavy wall in a liquid gas in-ground storage reservoir, which can be economically installed under the above adverse conditions, which can be properly aligned to permit accurate placement of a wall thereon, and which can be provided with means for accommodating very considerable changes `in radial dimensions due to thermal contraction at the extremely low temperatures involved.

Still another object is -to provide a footing and wall construction which is gas-and-liquid tight, and which is pre-stressed in such a 4manner as to oppose the stresses due to the extremely low temperatures existing under normal working conditions.

The specic nature of my invention, as well as -other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:

FIG. l is a schematic sectional elevation view of a storage tank embodying the invention;

FIG. 2 is an enlarged detail view similar to a portion of FIG. l, showing the footing structure;

FIG. 3 is a plan view of the storage tank showing the freeze pipes;

FIG. 4 is a plan view of a footing unit;

FIG. 5 is a sectional view taken transversely of the longitudinal axis of the unit of FIG. 4;

FIG. 6 is a side elevation of acentral portion of a footing unit;

FIG. 7 is an end elevation of a footing unit; and

FIG. 8 shows the junction -of two footing units.

FIG. 1 shows the general plan of a reservoir built according to the invention. The major portion of the excavation is made in an impervious stratum 2 of rock, or in any case, of hard, substantially impermeable ground formations, which may comprisea number of distinct strata. Overlying this is a depth of soil of other relatively permeable ground material which is typically naturally or articially saturated with water up to a level 4 higher than the base of the footing 8 described below. The ground level may be the natural ground level, or it may represent an elevated ground level due to the presence of soil which has been removed from the excavated portion and used to bank up part of the reservoir structure. A circle of refrigerating pipes 6, typically six-inch steel piping, surrounds the perimeter of the excavation, the piping being supplied, prior to filling the reservoir, with any suitable refrigerant at a temperature sufficiently low to maintain the soil for a distance of several feet on either side of the pipes in a frozen condition. After the soil has reached a suitable frozen condition and thickness, the excavation is commenced, until it attains the desired dimensions, the cylinder of frozen ground acting as a cotferdam.

After the excavation is formed, a ledge being cut back in the soil below the ground water level as shown at 7,

a bed of sand and grease S, typically about two inches thick, is mortared to the frozen ground, after which the blocks S', which serve as pad and footing, are installed by crane. These blocks are quite large, for example about 3 feet wide by 18 inches deep by 15 feet long. They are made of precast, reinforced, prestressed concrete so designed that thermal stresses will be practically cornpensated for by the prestressing. Keys and recesses are made on each block to key them in place. The greasesand bedding mixture 8 is selected to be of such composition that it will remain plastic at the low temperatures involved in the normal construction of the reservoir.

The footings 8 serve to support a wall 9, which typically extends from several feet below the ground level to several feet above the ground level, and in turn usually supports or is connected to a roofing structure 11 in any known fashion, this being not a part of the present invention. The wall 9 may be made of any suitable material, e.g., metal, but in practice the economic factors dictate the use of concrete, which is usually the least expensive material capable of giving satisfactory performance under the existing operating conditions. In the present installation, the wall 9 is made up of a plurality of precast, vertically prestressed concrete panels 9a, 9b, etc., as shown in FIG. 3. These are installed vertically by means of cranes, and are fitted edge-to-edge, using suitable keys as shown at 10, Where desired. The bottoms of the panels, constituting the entire wall bottom, rest in an annular trough 13 set into the top of the footings 8'; this trough is filled with arctic grease having a suitable cornposition for the temperature employed, which serves both as a lubricantbetween the footing and the wall, and also to provide a uid-and-gas-tight seal at low temperatures. Arctic greases having the necessary characteristics are known, and military specifications exist for the composition of such greases, composed of wax-oil mixtures.

After the entire wall is installed, it is tightly wrapped with many turns of steel wire or cable 14, under considerable tension, to further prestress the circular wall in the radial direction. Suitably, the wrapped exterior may then be coated with sprayedon mortar, shotcrete, or finished in any similar manner to both seal the exterior of the wall and to protect the cables against corrosion. Additionally, suitable insulation will be placed on the inside or the outside of the wall (or both) as desired and a exible liner or jacket completes the Wall. The precise wall construction and manner of prestressing are not per se the subject of the present invention.

As an aid in limiting the displacement of the footings 8', they may be tied back to the freezing pipes 6, as shown at 16.

It will be noted that the relationship between the footings and the wall is such that the Wall can contract radially inward when the temperature drops due to filling of the reservoir. The arctic grease 13 permits radial relative motion between the wall and the footings, while retaining the wall substantially in place.

As a possible alternative construction, the walls could be cast in place on the footings, once the footings have been set in place; however, this would he more diflcult than the precast panel method, because of the high temperature stressed due to the low temperature of the base and its environment at this stage of the process (-40 F.). When the tank is lled, the temperature is still further reduced to about 259 F., with great shrinkage of the concrete, which causes tensile stresses which could tear the entire structure apart. The above described prestressing process puts the concrete wall into an initial condition of stress which is opposite to that produced by the shrinkage due to the reduction of temperature, and thus acts to counteract the destructive effects of such shrinkage. The harmful effect of such stresses is minimized by making the wall as thin as possible, and in a typical case, for a reservoir which may be approximately 200 feet in diameter, the thickness of the wall will be approximately eight inches. The wall can be heldl to this thinness, and still retain the necessary strength, only by prestressing.

FIG. 4 shows a plan view of one of the footing sections. This section is made arcuate so that the assembly of the footings will define the circular perimeter of the wall which is placed above them. l A typical length, in this case, for a storage tank feet in diameter, is approximately` 19 feet for a footing section. For this size tank, the footing was three feet wide and two feet thick. It will be seen that such a massive section must be handled by heavy hoisting machinery.

At intervals in the annular trough 13 are set further ,rectangular recesses 21 to facilitate the assembly of the wall panels, the joints of which come over recesses 2l.V

Recesses 21 .are grouted after assembly. The annular recess 13 is filled with arctic grease after the wall is in place.

As shown in FIGS. 7 and 8, the adjoining ends of footing sections are preferably suitably keyed as shown at 22 and 23 to assist in providing yand maintaining alignment. The ends of the footings are buttered up with arctic grease as the sections are set in place, in order to exclude any possibility of moisture penetration before the temperature of the tank is lowered.

It will be apparentthat the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

Iclaim:

1. In the method of constructing a reservoir for storage at substantially atmospheric pressure of fluids at temperatures far below the freezing point of water, which method comprises the steps of prefreezing an annulus of liquid-bearing soil in the surface of the ground, excavating a storage pit in the ground within said annulus, and filling the reservoir with low-temperature liquid to be stored, the steps of (a) providing an exposed annular horizontal surface in the ground around the perimeter of said pit, below the ground level,

(b) laying a plastic bed of low-temperature grease and particles of a suitable inert ller material on said exposed surface,

(c) preforming a series of movable solid footing sec-` tions above ground,

(d) laying end-to-end on said bed said solid preformed footing sections to form a continuous footing on said annular horizontal surface,

(e) applying a low-temperature grease to the upper surface of said footing sections,

(f) erecting a wall on said footing sections, and

(g) installing a suitable cover sealed to said wall.

2. The invention according to claim 1, said exposed annular horizontal surface being dug below the watersaturated level of the ground.

3. The invention Iaccording to claim 1, wherein a lubricating layer of grease is maintained at all times between said wall and said footing sections.

4. The invention according to claim 1, said footings4 being of precast and prestressed concrete so stressed as to at least partially compensate for the thermal stresses due to the low temperature of the liquid in the reservoir.

5. The invention according to claim 1, said wall being formed of prefabricated wallsections lowered onto said footing sections.

6. An in-ground storage facility for liquids having a boiling point below the freezing temperature of ground water comprising means for prefreezing an annulus of liquid-laden soil adjacent to the upper perimeter of a large, open excavation in the ground,

(a) a horizontal footing surface formed in the ground adjacent tothe upper perimeter of said excavation,

(b) a plastic layer of low-temperature grease and a loose filler material laid in said footing surface, (c) a series of massive preformed1 solid footing sections laid end-to-end on said plastic layer with their upper surfaces in horizontal alignment, (d) a closed Wall resting on said footing sections and extending upwardly to above ground level, and (e) a vapor-tight roof over said excavation and joined by liquid-and-vapor-tight sealing means to the Wall of said excavation. 7. The invention according to claim 6, said horizontal footing surface being below the Water-saturated level of the ground.

References Cited by the Examiner UNITED STATES PATENTS McKenzie 61-.5

Jackson 6l36.l X

Goldtrap 61-.5 X 4Closner et al. 52-169 Schroeder 61-.5

Van Horn 61-.5 Proctor et al. 6l-.5

EARL I. WITMER, Primary Examiner. 

6. AN IN-GROUND STORAGE FACILITY FOR LIQUIDS HAVING A BOILING POINT BELOW THE FREEZING TEMPERATURE OF GROUND WATER COMPRISING MEANS FOR PREFREEZING AN ANNULUS OF LIQUID-LADEN SOIL ADJACENT TO THE UPPER PERIMETER OF A LARGE, OPEN EXCAVATION IN THE GROUND, (A) A HORIZONTAL FOOTING SURFACE FORMED IN THE GROUND ADJACENT TO THE UPPER PERIMETER OF SAID EXCAVATION, (B) A PLASTIC LAYER OF LOW-TEMPERATURE GREASE AND A LOOSE FILLER MATERIAL LAID IN SAID FOOTING SURFACE, (C) A SERIES OF MASSIVE PREFORMED, SOLID FOOTING SECTIONS LAID END-TO-END ON SAID PLASTIC LAYER WITH THEIR UPPER SURFACES IN HORIZONTAL ALIGNMENT, (D) A CLOSED WALL RESTING ON SAID FOOTING SECTIONS AND EXTENDING UPWARDLY TO ABOVE GROUND LEVEL, AND (E) A VAPOR-TIGHT ROOF OVER SAID EXCAVATION AND JOINED BY LIQUID-AND-VAPOR-TIGHT SEALING MEANS TO THE WALL OF SAID EXCAVATION. 